1. Field of the Invention
This invention relates to soybean oil-based composite formulations useful in the production of three-dimensional objects by the solid freeform fabrication method.
2. Description of the Prior Art
Solid freeform fabrication (SFF) is a method of, making shapes without molds. It is best known in its stereolithography forms as a method of rapid prototyping (U.S. Pat. No. 4,575,330). In stereolithography, a laser photopolymerizes successive thin layers of monomer to build up a solid object. Extrusion solid freeform fabrication (ESFF) was developed by the University of Arizona in collaboration with Advanced Ceramic Research (Tucson, Ariz.) as reported by K. Stuffle et al., [xe2x80x9cSolid Freebody Forming from Polymerizable Slurryxe2x80x9d, Solid Freeform Fabrication Symposium Proceeding, University of Texas, Austin, 60, (1993)]. The apparatus for implementing ESFF functions essentially as a three-dimensional (3D) pen plotter, wherein a slurry is extruded by a stepper motor depressing a syringe plunger and forcing the material through a needle. By moving the syringe over a computer-controlled path along each of the x, y and z axes, it is possible to create nearly any geometric figure [P. Calvert et al., xe2x80x9cChemical Solid Free-Form Fabrication: Making Shapes without Moldsxe2x80x9d, Chem. Mater., 9, 650, (1997)]. This method has the potential to produce geometrically complex composites that could not be made in any other way. Lombardi et al., (U.S. Pat. Nos. 5,906,863 and 5,932,290, both herein incorporated by reference) teach methods for the preparation of three-dimensional bodies by geometrically controlled deposition of layers of a liquid composition through a nozzle and onto a base. The composition comprises thermally-polymerizable components that polymerize upon heating.
Concerns for the stability of future petroleum supplies have stimulated much attention in the past few decades to feedstocks for polymers based on renewable resources [L. E. St. Peirre et al., Future Sources of Organic Materials, Pergamon, N.Y., (1980); I. S. Goldstein, Science, 817, 189 (1975); D. Swern, ed., Bailey""s Industrial Oil and Fat Products, Wiley, N.Y. (1979)]. The importance of natural products for industrial applications has recently become even more apparent as a result of increased social emphasis on the issues of the environment, waste disposal and depletion of non-renewable resources. United States agriculture produces over 12 billion pounds of soybean oil annually; and frequently in excess of one billion pounds remains unutilized. Development of economically feasible new industrial products from soybean oil, and commercial processes utilizing soybean oil, is highly desirable. Soy-based polymers could support global sustainability and provide an alternative to synthetic polymers for many manufacturing applications [R. P. Wool, xe2x80x9cDevelopment of Affordable Soy-based Plastics, Resins, and Adhesivesxe2x80x9d, Chemtech, 29: 44 (1999)].
Soybean oil is a double bond-containing triglyceride. These double bonds may be converted into the more reactive oxirane moiety by reaction with peracids or peroxides. In the past, epoxidized soybean oil (ESO), has mainly been used as plasticizer for PVC compounds, chlorinated rubber and PVA emulsions. Epoxy-containing soybean oil used as raw materials for the synthesis of new polymers suitable for liquid molding processes have been reported by Wool and coworkers [R. P. Wool et al., Polym. Prepr., (Am. Chem. Soc., Div. Polym. Chem.) 39:90 (1998); R. P. Wool et al., xe2x80x9cAffordable Composites from Renewable Sources (ACRES)xe2x80x9d, 216th ACS National Meeting, Boston, Aug. 23-27, 1998]. The structural strength of ESO-based composites can be enhanced by inclusion of mineral fillers and fibers that are now extensively used in the plastics industry to achieve desired properties or to reduce the price of the finished articles. Thus, it is relatively easy to formulate these composites to meet most commercial demands. In contrast to typical petroleum-based composite matrix resins such as vinyl esters, polyesters and epoxies, soy-based composites are optionally biodegradable; as plant oils, they contain functional groups that are readily attacked by lipase-secreting bacteria.
We have now discovered a series of epoxidized drying oil-based composite formulations useful in the production of objects by the solid freeform fabrication method. These formulations comprise (A) an epoxidized oil (primary resin); (B) a curing agent; (C) a fibrous filler; (D) a thixotropic agent and optionally (E) a secondary resin.
In accordance with this discovery, it is an object of this invention to provide a novel class of composites that can be shaped by the solid freeform fabrication method.
It is also an object of the invention to produce composites having a unique combination of properties meeting the demands of specific commercial applications.
Another object of the invention is to introduce a new use for vegetable oil and to expand the market for an agricultural commodity.
A further object of the invention is to produce composites that reduce the demand on petroleum resources and that are biodegradable.
These and other objects and advantages of the invention will become readily apparent from the ensuing description.